Differential cylinder-piston assembly



June 20, 1950 J. A, THlERRY 2,511,883

DIFFERENTIAL CYLINDER-PISTON ASSEMBLY Filed May 23, 194'? f?. f F7" .2.

INVENTOR,

BY w W @W ATT OEM E Y Patented June 20, 1950 DIFFERENTIAL CYLINDER-PISTON t AS SEBIBLY .lohnv Adams Thierry, South Milwaukee, Wis., as-

signorft'oBucyrus-Ere Company, South Milwaukee, Wis., acorporation of Delaware Application May'23, 1947, Serial No. 749,921

20 Claims.

My invention relates to new and useful improvements in double-'acting differential cylinderpiston assemblies, specifically those of the type that utilize fluid by-pass grooves on the surface of the piston and/or cylinder to effect one or more changes in the force-speed ratio of the assembly at different stages of relative travel of the piston and cylinder.

' The principal object of my invention is to provide an improved by-pass type double-acting differential cylinder-piston assembly, in which:

(1) The cylinder chamber is no longer than the length of the piston stroke (plus the piston thickness).

- (2) The cylinder chamber is of uniform crosssection forl its entire length.

(3) The piston is short, and of simple solid construction.

(4) A minimum of fluid by-pass grooves are employed.

(5) No enclosed longitudinal fluid passages are required.

(6) No Special -constrictions are required on the inner surface of the cylinder to change the force-speed ratio.

('7) The force-speed ratios are substantially the same for travel in either direction at any portion of the stroke.

(8) Assembly and disassembly is simple. (9) Cost of manufacture is reduced.

My invention consists in the novel parts and in the rcombination and arrangement thereof, which lare defined in the appended claims, and of which one embodiment is exemplified in the accompanying drawing, which are hereinafter particularly described and explained.

Throughout the description the same reference number is applied to the same member or to similar members.f f

' Figures 1 to 3 inclusive each constitute a longitudinal section of my invention, the piston assembly being shown in lthree successive positions, from lowest to highest, with respect to the'cylinder assembly which is fixed.

Figure 4 is a plan view of the piston assembly, taken along the line 4 4 of Figure 1.

y Referring now to Figures 1 to 3, we see that the interior of outer main cylinder II is divided by inner auxiliary cylinder I2 into main chamber I3 and auxiliary chamber I4; main chamber I3 being the space between these cylinders, and having a greater cross-sectional area than aux-y iliary chamber I4.

For ease in manufacture and assembly, the main and auxiliary cylinders preferably have a common bottom I5, but separate tops I6 and Il 2 f respectively. Top I6 nts partly over and around top I1 of auxiliary cylinder I2 to hold itin place.v

Fluid port I8A in bottom I5 leads intc auxiliary chamber I4, and fluid port I`9` inA top I 6 leads into main chamber I3.

My piston consists of main piston 2l) which' has fluid-tight sliding contact with the inside of main cylinder II and the outside of auxiliary cylinder I2, and auxiliary piston 2I which has fluid-tight sliding contact with theinside of aux; iliary cylinder I2. Extending upwardly froxnf` main piston 20 are preferably two piston rods 22 which extend out through fluid-tight openings in top I6 of main cylinder II. 'Extending upwardly from auxiliary piston 2I is piston rod 23 which passes out through a fluid-tight open-i ing in topv I1. vPiston rods 22 and V23 are'pref-L erably located 'inthe same vertical 'plane v and are connected outside the assembl'ytd the end of a single rod 24' which is preferably aligned with inner rod 23:.l Likewise'p'istons 20 and 2| are preferably aligned to'lie in the same'hori'- zontal transverse plane. Stops 25at'ea'ch'cnd of pistons 2U and 2| prevent ythe ends of the pistons from abutting the vendsfof the cylinders.

On `the inside of the 'walls' enclosing main1 chamber I3 (preferably on the inside surface of main cylinder II) there are lengthwise grooves 26; and on the inside surface of auxiliary cylinder I2 there are lengthwise grooves 21. lGrooves4 26 and 2l are located at'endsof these `'respective chambers that are opposite to the ends invvhichv are located fluid ports, I 8 and I9 into these chambers.

Fluid ports 28 at'fthe lower end of grooves 21 in auxiliary cylinder I2 provide `a passage be v tween chambers I3 and I4.

Grooves 26 inside main cylinderl Il, grooves 2l' inside auxiliary cylinder I2, and ports 28 through auxiliary rcylinder I2'are "so positioned relative to each other that grooves 26 will byy pass around piston 20 ifv and only if grooves 21 are blocked from lby-passingaround' auxiliary piston 2`I, and vice versa, and that when the piston of one chamber is by-'passed the internal.

port functions as' the pressurel inlet of said other chamber whenever fluid is admitted under pres'- sure to said one chamber through its external port, and as the exhaust port of said one chamber whenever fluid is admitted under pressure to said other chamber through its external port; and that when the piston of said 'one chamber is no longer by-passed, the internal port func whenever fluid is admitted under .pressure through the external ".port of said one chamber,

and as the pressure inlet of said one chamber whenever fluid is admitted under pressure through the external port of said other chamber. The relative length of each set of grooves is determined by the relative length of travel for each oi the, speeds which they produce.

It will, be seen from the foregoing description of my invention that I have in effect two pistons operating in two respective cylinders. That is; to say, my main piston 2G operatesv inV a main chamber I3 the walls of which are-the inner surface of my main cylinder II plus the outer surface of auxiliary cylinder |12,I and@` my auxiliaryV cylinder I2 It will be noted that my auxiliary piston 2l v and its cooperating auxiliary chamber I4 have I a smaller effective pressure-area than that of my main-piston Zllr and itsmain chamber I3.

The operation of my cylinder-piston assembly is` as.y follows:

Assumev the apparatus to be in the position shown in Figure 1. PressureY ihiidv is admitted, throughA port t8, intov the lower end of the,- auxiliary chamber I4, j-ust, below auxiliary piston 2|, setting` upv pressure against the cross-sectional area of'v this piston. Under the influence4 of this pressure, piston 2I- and its piston-rod 23 move upward-ly raipidly withV slight force, carrying with them main pistonA 2,0. and` its piston-rods 22.

Meanwhiley exhaust, from. the upper end of auxiliary chambers,- Illf passes through ports 28 into main; chamberv I3,- pressures aboveand. below main` piston 20.-areeql1a1ized throughy grooves 26,; and, exhaust fromthe; upper endv of main chamber I3 passes" out` through port IIS` at: the top or the;` cylinder:

Turning nowv toflligu-refS',A when pistons 20 and 2 l1' have reached the-position shown in this ligure.- piston`- 2-I has uncovered, l'fllfty 23 I and` hencefluid i's-now-free to pass througmportslintothe low` el?V portion ormain chamber I3, 'setting uppressure against-the lower face or main piston 2D around which uidis no longer free to pass.v Since pressures above and bel-ow auxiliary pistonl M are equalizect through grooves` 2l, the effective pressure areanowbecomes. the.A area,I i theface of main, piston` 2l),` which; is:- considerably more than the-area, of the face of auxiliary, piston 2l. Accordingly pistons;v 20. and, 2| and,A their rods. 22 and'= 23- now move upwardly slowlywith considerably greater force than in the rst portion of thei stroke Exhaust from tha upper endA of"y main chamberA Ill;- passes out through. portK I 9- atrtheftop of the cylinder.

Figure Zishows-the assembly with the-,pistons in; the; intermediate; position just` as they pass fromlthehigh to,y the low-speed-portions orA their travel.`

The reverse motion (downward), is similar,v the' initialand lrlrxal pressure being against, the; upper instead ofV they-lower faces of pistonsf and 2-I rev spectively. FluidY under, pressure is admitted, through port I9, into` the upper end` of main chamber Hf, and the exhaustfromfthelowerl end of auxiliary chamber I2passes out;l throug-h port t8;A Now, however, theztravel is slow and forceful at;the=beginning^of' thetraveL andV isv fast and less-'forceful at the endzof-l the travel. Both speeds are. slightlyr higherV and less, forcefulA than the correspomiing'speeds` of the upward stroke, due t'o-.t-he piston rodsy which; reduce slightly'the effecti-vepressurexarea of the pistons.

Having now describedand illustrated one form pistons, nevertheless my invention is not to be so l0 limited being equally applicable to assemblies vemploying any number lof concentric cylinders and pistons to produce a like number or" speeds, the, external ports leading always preferably to the innermost' and outermost chambers.

Furthermore, it` will be readily seen that the lay-pass grooves inl a chamber (such as chamber I3 of oy-pass 1 to 3) between walls formed by the inner surface of one cylinder and the outer surface of another cylinder, may be located on eitherl wallfwithout affecting the operation of the assembly, and my claims arel to be so interpreted.

I- claim:

1.` In. a cylinder-pistonassembly, the combination of; a main. cylinder having a: main chamber ,ith main; piston therein ofrelatively large effec tive pressure-area; an auxiliary cylinder inside and conterminous with the mainl cylinder and, having: an auxiliary chamber with an auxiliary piston therein ofv relatively small effective pres sure. area; a piston-y rod; means operatively connecting the; two pistons tov the. pistonrod; means for alternatively admitting fluid under pressure to the main chamber or to the auxiliary chamben, simultaneously permitting exhaust from the other chamber; meansforautomaticallybypassing Huid past one of the pistons whenever the piston-rod is near one end of its stroke;` and means-for automatically by-passing fluid past the other piston at another stage of said stroke.

2.. A cylihder-pistonl assembly, according to claim l, further characterized by the iact that one or another of the ley-pass means is always blckedz 3. A cylinder-piston assembly, according to claim- 1', further characterized by the fact that the` by-pass means for the' main piston includes at least one longitudinal groove i-n a wall of the main chamber, which groovefis uncoverable by relative motioni of the, piston-rod andthe main cylinder.

4; A` cylinder-piston assembly, according to claim 1, further ch-aracterized'by the fact that the Icy-pass means for the auxiliary piston in-I cludes at leastl one longitudinalv groove in a wallof the auxiliarylchamber, which groove is uncoverableby relative motion ofl the piston-rod and the auxiliaryY cylinder.

5. A cylinder-piston assembly, according to. claim` 1.,., further characterized by the fact that thei by-pass nleansY for the auxiliary and main pistons includes respectively at least one longitudii-nal groove.- inkv the i-nterior surface of the auxiliary cylinder'and at least one longitudinal-groove in ,the .eateries surface ofthe auxiliary cylinder.

6. A cylinder-piston assembly, accordingl to claim 1. further characterized by the fact that theY means operatively. connectingl the two pisons to `the pistone-rod includes: a piston-red connested to the auxiliary piston; af piston rod connectedto. the'main piston; and means-connectv` ing the.- twolastfernentioned piston rods to the first-mentioned piston rod.

71'. A;v cylinder-piston assembly, accordingA to claim 1', urthercharacterized-by the fact that the main and'auxiliary pistons lie in substantially the same plane transverse' kto 'their' direction`r` bfiA traveli 8., A v'cylinder-piston assembly, according toV and their respective chambers are connected by afluid port in the wall of the auxiliary-cylinder'. v-`ll0. A cylinder-piston assembly-*according to claim 1, further characterized by the fact that whenever the by-pass means of one piston bypasses said one piston, the by-pass means of the other piston will not by-pass said other piston.

11. A cylinder-piston assembly, according to claim 1, further characterized by the fact that the means for admitting fiuid under pressure to the main and auxiliary cylinders includes: an external port at one end of the main chamber; an external port at the opposite end of the auxiliary chamber; and an internal port providing passage between the main and auxiliary cylinders so positioned that: when the piston of one chamber is by-passed, the internal port functions as the pressure inlet of said other chamber whenever uid is admitted under pressure to said one chamber through its external port, and as the exhaust port of said one chamber whenever fluid is admitted under pressure to said other chamber through its external port; and that when the piston of said one chamber is no longer by-passed, the internal port functions as the exhaust port of said one chamber whenever fluid is admitted under pressure through the external port of said one charner, and as the pressure inlet of said one chamber whenever fluid is admitted under pressure through the external port of said other chamber.

12. In a cylinder-piston assembly, the combination of: a main cylinder and an associated auxiliary cylinder of lesser diameter; a main piston having outwardly a sliding contact with the interior surface of the main cylinder and the exterior surface of the auxiliary cylinder; an auxiliary piston having outwardly a sliding contact with the interior surface of the auxiliary cylinder; a piston-rod operatively connected to the main and auxiliary pistons; and a system of iiuid conduits providing a by-pass past the area of contact between the main piston and one of the cylinders, and a by-pass past the area of contact between the auxiliary piston and its cylinder, these by-passes being opened and closed automatically by the relative motions of the pistons and cylinders, and being so positioned that whenever one by-pass is open the other by-pass is closed.

13. A cylinder-piston assembly according to claim l2, further characterized by the fact that the system of fluid conduits includes at least one longitudinal groove in the interior surface ofthe main cylinder, which groove is uncoverable by relative motion of the piston rod and the main cylinder.

14. A cylinder-piston assembly accordingto claim 12, further characterized by the fact that the system of fluid conduits includes at least one longitudinal groove in the interior surface of the auxiliary cylinder, which groove is uncoverable by relative motion of the piston rod and the auxiliary cylinder.

15. A cylinder-piston assembly, according to claim 12, further characterized by the fact that the system of fluid conduits includes respectively at least one longitudinal groove in the interior surfacejof the auxiliary cylinder and at least one? longitudinal groove in the exterior surface o f the the same vplane transverse to their direction ofiy travel.v v

17.1%' cylinder-piston assembly according to'l claim 12", further characterized by the fact that thehmain and auxiliary cylinders are concentric?,

conterminalg-and substantially the'same lengthasr the stroke of the piston-rod relative to the main cylinder.

18. A cylinder-piston assembly according to claim 12, further characterized by the fact that the system of uid conduits includes: an external port at one end of the main cylinder chamber; an external port at the opposite end of the auxiliary cylinder chamber; and an internal port providing passage between the main and auxiliary cylinder chambers so positioned that: when the piston of one chamber is by-passed, the internal port functions as the pressure inlet of said other chamber whenever iiuid is admitted under pressure to said one chamber through its external port, and as the exhaust port of said one chamber whenever fluid is admitted under pressure to said other chamber through its external port; and that when the piston of said one chamber is no longer by-passed, the internal port functions as the exhaust port of said one chamber Whenever fluid is admitted under pressure through the external port of said one chamber, and as the pressure inlet of said one chamber whenever uid is admitted under pressure through the external port of said other chamber.

19. In a cylinder-piston assembly, the combin-ation of a main cylinder and an associated auxiliary cylinder of lesser diameter; a main piston having outwardly a fluid-sealed sliding contact with the interior surface of the main cylinder and the exterior surface of the auxiliary cylinder; `an auxiliary piston having outwardly a fluid-sealed sliding contact with the interior surface of the auxiliary cylinder; a piston-rod operatively connected to the main and auxiliary pistons; means for the introduction of pressure-Huid into the cylinders, to actuate relative reciprocation of the pistons in one direction; means for the introduction of pressure-fluid into the cylinders, to actuate relative reciprocation of the pistons in the other direction; by-pass means, to break the fluid seal between the main piston and one of the cylinders, automatically rendered effective by the relative position of the piston and said one of the cylinders during a part of the relative reciprocation of the main piston in each direction, and automatically rendered ineffective by the relative position of the main piston and said one of the cylinders during another part of the relative reciprocation of the main piston in each direction; bypass means to break the fluid seal between the auxiliary piston means and its cylinder, automatically rendered effective by the relative position of the auxiliary piston and its cylinder during -a part of the relative reciprocation of the auxiliary piston in each direction, and automatically rendered ineffective by the relative position of the auxiliary piston and its cylinder during another part of the relative reciprocation of the auxiliary piston in each direction; whereby the main piston is relieved of fluid pressure and the auxiliary piston is subjected to fluid pressure during a portion of the reciprocation in each d1- rec-tion, and the auxiliary piston is relieved o i iiuid pressure. and` the mainv piston is; subjected to uid pressure during another portionof' the reciprocation in eachv direction,

20. A cylinder-piston assembly according t0 claim 19, further characterized by the fact that the byepass means that functions to break; thek uid seal between one of the pistons and onef the cylinders comprises at least one duct extending from one point on the surface of said oneof l0 thecylinders to another point thereon longitudi-v nally spaced from the rst pointlsaidA duct being effective when these two pointsbracket said one;

of the pistons, and ineffective when these two points' do not bracket said one of the pistons JOHN ADAMS THIERRY.

REFERENCES CITED FOREIGN PATENTS Country Date Germany Jan. 27, 1925 NunzdoerY 

